Transformer assembly

Abstract

The present invention relates to a transformer assembly ( 1 ) and a process for manufacturing same. The transformer ( 1 ) comprises a primary winding ( 5 ) wound on a PCB ( 9 ) and a secondary winding ( 7 ) mounted adjacent to the primary winding. The primary winding comprises a spiral coil, for example of wire or insulated wire, wound on the PCB. Gate drive windings ( 31, 33 ) are incorporated in the PCB ( 9 ) and there is therefore very close coupling between the primary winding and the gate drive windings. Furthermore, the secondary winding ( 7 ) is a center-tapped secondary having two halves. A flux balance winding ( 13 ) is provided to connect the two halves of the center-tapped secondary winding ( 7 ) and minimize leakage inductance thereby reducing power loss and spiking effects and obviating the need for complex control arrangements.

1. A transformer assembly comprising a magnetic core, a primary winding and a secondary winding, wherein the primary winding further comprises a spiral winding of insulated wire, the spiral winding having a pair of connected spiral sections, the first spiral section winding inwardly and gradually decreasing in diameter to a connection branch with the second spiral section and the second spiral section winding outwardly and gradually increasing in diameter from the connection branch so that both ends of the winding are accessible at the periphery of the winding, in which there is provided a substrate upon which the primary winding is wound and each spiral section is wound on one side of the substrate, the substrate being substantially horseshoe shaped with an open channel for through passage of the primary winding. 
     
     
       2. A transformer assembly as claimed in  claim 1  in which the wire is wound flat against the substrate. 
     
     
       3. A transformer assembly as claimed in  claim 1  in which the secondary winding is implemented using folded foil techniques. 
     
     
       4. A transformer assembly as claimed in  claim 1  in which magnetic core further comprises a pair of E-cores mounted face to face with the arms of the E-cores opposing each other. 
     
     
       5. A transformer assembly as claimed in  claim 1  in which the magnetic core further comprises an E-core and a planar core with the arms of the E-core facing the planar core. 
     
     
       6. A transformer assembly comprising a magnetic core, a primary winding and a secondary winding, wherein the primary winding further comprises a spiral winding of insulated wire, the spiral winding having a pair of connected spiral sections, the first spiral section winding inwardly and gradually decreasing in diameter to a connection branch with the second spiral section and the second spiral section winding outwardly and gradually increasing in diameter from the connection branch so that both ends of the winding are accessible at the periphery of the winding, in which there is provided a printed circuit board upon which the primary winding is wound and each spiral section is wound on one side of the printed circuit board, in which the transformer further comprises a gate drive turn implemented as a layer of a printed circuit board. 
     
     
       7. A transformer assembly as claimed in  claim 6  in which the outer faces of the printed circuit board are implemented as shields. 
     
     
       8. A transformer assembly comprising a magnetic core, a primary winding and a secondary winding, wherein the primary winding further comprises a spiral winding of insulated wire, the spiral winding having a pair of connected spiral sections, the first spiral section winding inwardly and gradually decreasing in diameter to a connection branch with the second spiral section and the second spiral section winding outwardly and gradually increasing in diameter from the connection branch so that both ends of the winding are accessible at the periphery of the winding, in which there is provided a shield interposed between the primary winding and the secondary winding, the shield being a unitary shield substantially H-shaped having a cross bar and two pairs of legs projecting outwardly from the cross bar, the cross bar of the shield being positioned above the transformer adjacent the substrate and a pair of the legs of the shield protruding downwardly between the primary winding and the secondary winding on either side of the substrate. 
     
     
       9. A transformer assembly as claimed in  claim 8  in which the shield interposed between the primary winding and the secondary winding is connected to an outer face shield of a printed circuit board. 
     
     
       10. A transformer assembly comprising a magnetic core, a primary winding and a secondary winding, wherein the primary winding further comprises a spiral winding of insulated wire, the spiral winding having a pair of connected spiral sections, the first spiral section winding inwardly and gradually decreasing in diameter to a connection branch with the second spiral section and the second spiral section winding outwardly and gradually increasing in diameter from the connection branch so that both ends of the winding are accessible at the periphery of the winding in which there is provided a flux balance winding located intermediate the secondary winding and an adjacent magnetic core section. 
     
     
       11. A transformer assembly as claimed in  claim 10  in which the flux balance winding is located intermediate the secondary winding and the primary winding. 
     
     
       12. A transformer assembly comprising a magnetic core, a primary winding, a centre tapped secondary winding having a pair of physically separated halves, the transformer further comprising a flux balance winding to reduce effective leakage inductance between the two halves of the centre tapped secondary. 
     
     
       13. A transformer assembly as claimed in  claim 12  in which the flux balance winding is located intermediate the secondary winding and an adjacent magnetic core section. 
     
     
       14. A transformer assembly as claimed in  claim 12  in which the flux balance winding is a unitary winding extending across the PCB and in which the flux balance winding is insulated around the area of the winding adjacent the PCB. 
     
     
       15. A transformer assembly as claimed in  claim 12  in which there are provided a pair of separate flux balance windings, one of which is associated with one half of the centre tapped secondary winding and the other of which is associated with the other half of the centre tapped secondary winding.